A variety of woven and nonwoven webs including spunbond (SB) and spunbond-meltblown-spunbond (SMS) fabrics are made using hydrophobic synthetic fibers. The webs are used for a wide variety of applications including diaper back sheets, cuff materials, surgical drapes, surgical gowns, nonwoven food service apparel and other applications in which barrier properties such as moisture permeability, liquid retention, air permeability and vapor permeability are important. Common materials for the fibers used to make such webs are polymers such as polypropylene and polyethylene. While these polymers are hydrophobic to a degree, the barrier properties of webs made from the fibers are insufficient for some applications. Accordingly, it has been necessary to apply surface finishes to the webs to improve their barrier properties for certain end uses.
Surface finishes applied to hydrophobic fibers and webs are not very durable and tend to erode or rub off the material during use. This is of particular concern to the medical field where hydrophobic webs find use as fabrics, sheets and various other articles to block transmission of body fluids and other substances between the medical personnel and the patient and vice-versa.
Another problem associated with coated fabrics is that the fabrics tend to exhibit rough surface feel characteristics. Fabrics having softer surface feel properties tend to be less durable. In applications which require a clean environment, abrasion of the less durable fabric garments may cause fibers in the outer layers of such fabrics to break away from the bulk of the fabric and form fiber pills which may detach from the surface and contaminate the environment. In applications requiring protection of the wearer from large amounts of dusts or fibers, the rough surface of the fabric garment can entrap the dusts or fibers and upon removal of the garment, the trapped dusts or fibers may enter the breathing zone of the wearer.
It is therefore an object of the invention to provide synthetic fibers which exhibit hydrophobic characteristics.
Another object of the invention is to provide webs containing synthetic fibers which exhibit hydrophobic characteristics.
A further object of the invention is to provide a method for decreasing the surface energy of hydrophobic fibers.
An additional object of the invention is to provide a fibrous web with enhanced barrier properties.
Still another object of the invention is to provide a fibrous web containing hydrophobic fibers which exhibit decreased surface energy.
Yet another object of the invention is to provide hydrophobic fibers for a web which give the web substantially permanent barrier properties which are not subject to removal by wear, abrasion or laundering.
Another object of the invention is to provide hydrophobic fibers for use in making fibrous webs with reduced air permeability, increased strength and increased softness.
With regard to the above and other objects, and in accordance with its more general aspects, the invention provides an article which comprises a mixture of polymer selected from the group consisting of polyolefins and polyesters and an additive having the structure R.sup.1 --A--Si(R.sup.2 R.sup.3)--O--(Si(R.sup.4 R.sup.5)--O).sub.n --Si(R.sup.6 R.sup.7)--A--R.sup.8 wherein the R.sup.1 and R.sup.8 units are selected from the group consisting of alkyl, aryl, alkylaryl groups and acyl and arylacyl derivatives of an aliphatic or aliphatic/aromatic mono-acid with a molecular weight of from about 250 to about 600 daltons, A is selected from the group consisting of --O--, --NH--C(O)--NH--(CH.sub.2).sub.3 --, and --C(O)--NH--(CH.sub.2).sub.3 --, R.sup.2, R.sup.3, R.sup.6 and R.sup.7 are selected from the group consisting of CH.sub.3, C.sub.2 H.sub.5, C.sub.3 H.sub.7, and C.sub.4 H.sub.9, R.sup.4 and R.sup.9 are selected from the group consisting of CH.sub.3, C.sub.2 H.sub.5, C.sub.3 H.sub.7, and (CH.sub.2).sub.I -- C.sub.j F.sub.2j+1, wherein I is from 0 to 3 and j is an integer from 1 to 3, and n is an integer from 7 to 70. In one embodiment, the article is a fiber which can be incorporated into a web or sheet such as a nonwoven or woven fabric.
In accordance with another aspect of the invention, a method is provided for making a shaped polymeric article such as a fiber which comprises mixing a polymer selected from the group consisting of polyolefins and polyesters with an additive having the structure R.sup.1 --A--Si(R.sup.2 R.sup.3)--O--(Si(R.sup.4 R.sup.5)--O).sub.n --Si(R.sup.6 R.sup.7)--A--R.sup.8 wherein R.sup.1 and R.sup.8 are selected from the group consisting of alkyl, aryl, alkylaryl groups and acyl and arylacyl derivatives of an aliphatic or aliphatic/aromatic mono-acid with a molecular weight of from about 250 to about 600 daltons, A is selected from the group consisting of --O--, --NH--C(O)--NH--(CH.sub.2).sub.3 --, and --C(O)--NH--(CH.sub.2).sub.3 --, R.sup.2, R.sup.3, R.sup.6 and R.sup.7 are selected from the group consisting of CH.sub.3, C.sub.2 H.sub.5, C.sub.3 H.sub.7, and C.sub.4 H.sub.9, R.sup.4 and R.sup.5 are selected from the group consisting of CH.sub.3, C.sub.2 H.sub.5, C.sub.3 H.sub.7, and (CH.sub.2).sub.I --C.sub.j F.sub.2j+1, wherein I is from 0 to 3 and j is an integer from 1 to 3, and n is an integer from 7 to 70, and molding the mixture into the shaped polymeric article. The molding step may be an extrusion or casting step such as in the manufacture of fibers.
Articles according to the invention such as fibers exhibit substantially enhanced hydrophobicity. Accordingly, a web made from fibers incorporating the compositions of the invention, in whole or in part, is expected to exhibit improved barrier properties. Webs including fabrics containing the fibers can exhibit barrier properties which are comparable to conventional fabrics at a much lower weight. Hence, the denier of fibers used to make the fabric may be reduced resulting in savings in fabric cost. Fabrics containing the fibers are also expected to exhibit improved durability as compared with conventional barrier fabrics, have increased opacity, reduced air permeability and a softer texture.
The invention is especially well adapted for use in making fibers based on hydrophobic polymers selected from the group consisting of polyolefins such as polypropylene (PP), polyethylene (PE), polybutylene (PB), polystyrene (PS), and mixtures thereof and polyesters such as polybutylene terephthalate (PBT), polyethylene terephthalate (PET) and mixtures thereof. The invention is particularly advantageous for polyolefin-based fibers, most preferably PE or PP.
The polymer comprises a major portion of the composition which may include conventional additives such as flame retardants, pigments, fillers, antioxidants, UV stabilizers and the like. Accordingly, the composition may contain from about 90 to about 99.9% by weight of the polymer with the conventional additives being used in amounts sufficient to confer the desired properties.
The additive mixed with the polymer has the structure R.sup.1 --A--Si(R.sup.2 R.sup.3)--O-- (Si(R.sup.4 R.sup.5)--O).sub.n --Si(R.sup.6 R.sup.7)--A--R.sup.8 wherein the R.sup.1 and R.sup.8 units are selected from the group consisting of alkyl, aryl, alkylaryl groups and acyl and arylacyl derivatives of an aliphatic or aliphatic/aromatic mono-acid with a molecular weight of from about 250 to about 600 daltons, A is selected from the group consisting of --O--, --NH--C(O)--NH--(CH.sub.2).sub.3 --, and --C(O)--NH--(CH.sub.2).sub.3 --, R.sup.2, R.sup.3, R.sup.6 and R.sup.7 are selected from the group consisting of CH.sub.3, C.sub.2 H.sub.5, C.sub.3 H.sub.7, and C.sub.4 H.sub.9, R.sup.4 and R.sup.5 are selected from the group consisting of CH.sub.3, C.sub.2 H.sub.5, C.sub.3 H.sub.7, and (CH.sub.2).sub.I --C.sub.j F.sub.2j+1, wherein I is from 0 to 3 and j is an integer from 1 to 3, and n is an integer from 7 to 70.
When the polymer to which the additive is added is PP, it is preferred that R.sup.1 and R.sup.8 be hydrogenated abietic acid, A is --O--, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, and R.sup.7 be CH.sub.3, and n be an integer from 15 to 70. For use with polyethylene, it is preferred that the R.sup.1 and R.sup.8 units be selected from the group consisting of derivatives of dehydroabietic acid, dihydroabietic acid, abietic acid, tetrahydroabietic acid, pimaric acid and palustric acid, wherein A is --C(O)--NH--(CH.sub.2).sub.3 --, wherein R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, and R.sup.7 are CH.sub.3, and wherein n is an integer from 20 to 60.
When the polymer is PS, it is preferred that R.sup.1 and R.sup.8 be derivatives of abietyl, A be --O--, R.sup.2 --R.sup.7 be CH.sub.3, and n be from 15 to 70. When the polymer is PET, the preference is that R.sup.1 and R.sup.8 be derivatives of abietyl, A be --O--, R.sup.2 --R.sup.7 be CH.sub.3, and n be from 15 to 70.
The additive is intimately mixed with the polymer to obtain a substantially homogeneous mixture of polymer and additive. Mixing may be accomplished by any of the methods known or hereafter known in the art for mixing additives with polymers. For example, the additive and polymer may be melt-blended together or they may individually be dissolved in one or more compatible (i.e., miscible) solvents, the solvent solutions mixed together and the solvents removed by evaporation, extraction, distillation and the like, producing a polymeric composition containing the additive. Suitable solvents for polypropylene and the additive include, but are not limited to, orthodichlorobenzene and trichlorobenzene.
The additive may be mixed with the polymer in an amount ranging from about 0.05 to about 5% by weight or more. For most applications an effective amount of additive will range from about 0.05 to about 3.0% by weight, and from about 0.1 to about 0.5% additive by weight of the total composition will generally be sufficient to materially improve the hydrophobicity of the composition. The additive may be supplied all at once to the polymer or a concentrate containing polymer and additive may be formed and the concentrate added to additional polymer. For example, the additive may be mixed with the polymer to provide a concentrate containing about 2% by weight additive and the concentrate may then be melt-blended with additional polymer to provide a composition containing from about 0.1 to about 0.5% by weight additive.
In a preferred embodiment, the composition is prepared by feeding the polymer in solid particulate or pellet form to an extruder hopper and adding the additive to the polymer in the extruder. Since the additive is typically in liquid form and the polymer is typically a solid at room temperature, the additive may be fed into the extruder at a variety of locations. It is preferred, though not required, to first melt the polymer before mixing the additive with the molten polymer. For example, solid polymer particles may be fed by means of a hopper into an extruder where it is advanced through a melting stage and the additive is injected into the molten polymer at a point in the extruder which can provide substantial and intimate blending of the additive and polymer. Alternatively, the polymer and additive may be mixed with one another in a thermostatted vessel wherein the components are maintained in liquid form during mixing.
The mixture of polymer, additive and other additives may be conducted directly to a mold or extruder in liquid form or after a homogeneous mixture of the two components is obtained, the composition may be cooled, solidified and granulated or chopped before feeding solid particles containing the composition to an extruder or molding apparatus to form articles or fibers containing the composition. For example, the composition in molten form containing the polymer and additive may be fed through an orifice of an extruder to produce an elongate rod which is then cooled and chopped or cut into pellets. The pellets may then be used in a molding machine to produce a shaped article or submitted to an extruder containing a spinnette to produce fibers or filaments.
A fiber producing extruder typically contains spinning orifices in a spinnerette which form unitary filaments having a substantially uniform cross sectional diameter along substantially the entire length of the filaments. The filaments produced by such an extruder may be drawn and texturized and then wound on a spindle or roll, and then used to weave a fabric or a nonwoven fabric using a melt-blown or a spunbond process.
In a typical spunbond process, a polymeric composition which may contain one or more polymeric materials, processing aids, plasticizers and the like is fed to a hopper, then to an extruder and metering pump and to a spin box wherein filaments are spun through a moving spinnerette onto a continuous foraminous surface such as a belt, plate or screen. The spinnerette contains openings arranged in one or more rows to form a curtain of filaments which is directed to a quench chamber. In the quench chamber the filaments are contacted with air or other cooling fluid under a low pressure. As the filament curtain is quenched it is directed through a narrow chamber at the lower end of the quench chamber whereby the cooling fluid attains a high velocity. After exiting the quench chamber, the filaments are collected on the moving foraminous surface such as an endless screen or belt to form a non-woven web.
During the spinning operation, the spinnerette is moving across the collecting surface so that the filaments extruded from the spinnerette are laid down in random orientation on the collecting surface. As the filaments are deposited, they cool and solidify into a fibrous web. Because the filaments are still in a softened form when they are extruded from the spinnerette, the fibers tend to bond to one another at their overlaps and intersections. Additional bonding may be achieved by use of binders or by heating and pressing the fibrous web using an embossed, heated nip roll in order to melt the fibers together and to modify the texture of the web.
Methods for making spunbond fabrics are described in U.S. Pat. No. 3,692,618 to Dorschner et al, U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,989,788 to Estes, Jr. et al. and U.S. Pat. No. 4,340,563 to Appel et al., incorporated herein by reference as if fully set forth.
In a melt-blown process, a polymeric composition is fed to a hopper, then to an extruder and metering pump to a spin box. The spin box contains a spinnerette and a source of high pressure fluid such as air to surround and entrain the polymeric material and to educt the filaments from the orifices of the spinnerette. As the filaments are educted, they are deposited on a moving foraminous surface such as a belt or screen. The high pressure fluid spreads the polymeric stream and forms microfibers which are randomly deposited on the moving web to form a melt-blown layer of fibers. Methods for making melt-blown webs are known in the art and are described in U.S. Pat. No. 3,849,241 to Buntin et al., incorporated herein by reference as if fully set forth.
While not desiring to be bound by theory, it is believed that the additive lowers the surface energy of the polymeric composition upon solidification thereof because at least a portion of the additive has migrated to or near the exposed surface the article containing the composition thereby changing its surface characteristics. It is also believed that the surface of the article material exhibits a decreased surface energy due to the presence of a siloxane midblock of the additive at the surface of the article. Because the additive is intimately mixed with the polymer rather than being applied as a surface treatment on the article, the effect of the additive is not significantly diminished by wear or abrasion.
Furthermore, the additive is substantially non-fugitive from the composition and, consequently, the surface energy of an article containing the composition is substantially permanently lowered. The substantial non-fugitive nature of the composition is due, at least in part, to the presence of the hydrocarbon end blocks of the additive. The hydrocarbon end blocks provide anchors in the polymer for the midblock which exists near or at the surface of the article due to migration of the additive to the surface of the article during the cooling step.
The decrease in surface energy of the composition enables a variety of beneficial uses for the material. For example, the material may be formed into films, fibers, molded articles and the like.
With the decrease in surface energy, there is often also a reduction in the coefficient of friction for shaped articles containing the composition of the invention. Therefore, articles according to the invention may be useful as bearings and in other non-stick applications where surface-to-surface movement with a minimum of friction is required.
The additive itself is also useful as a film extrusion processing aid, lubricant or anti-blocking agent. Accordingly, when the additive is introduced into and is intimately mixed with the polymer, extrusion of the composition is accomplished with lower energy input and greater ease.
The following nonlimiting examples illustrate certain other aspects of the invention and its various embodiments.